Digital image overlay in image intensified and day sight system

ABSTRACT

An optical system for overlaying a first image of a scene and a second image includes a first imaging device providing the first image, a second imaging device with an image display and collimation optics providing the second image, and a waveguide. The waveguide has a first diffraction grating configured to receive the first image, a second diffraction grating configured to receive the second image, and a guide portion disposed between the first diffraction grating and the second diffraction grating configured to convey the second image to the first grating. The first diffraction grating is configured to overlay the first image and the second image.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to European Patent Application serialnumber 18170704.3, filed May 3, 2018, entitled “Digital Image Overlay inImage Intensified and Day Sight System,” which is incorporated byreference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates to an optical device, and moreparticularly, is related to enhanced analogue vision devices.

BACKGROUND OF THE INVENTION

Specialized analogue optical devices such as night vision (imageintensifying (I²)) goggles and telescopic sights, together with thermalcameras and digital displays provide images and information to a viewerthat is both separate and distinct. However, the images produced by suchdevices contain complimentary information that, in the context of ascene, may be difficult for the viewer to assimilate when viewed asseparate channels. Previous devices have combined such images withanother specialized image or a visible light image by the design ofbespoke but standard optics to perform image injection. However, theimages provided by these devices have either made it difficult for theviewer to discriminate between the two images, or have required bespokeoptics in situ to accomplish this. In particular, the combined imagesmay be limited to a narrow color range, making the combined imagesdifficult for the viewer to differentiate the two images. Furthermore,such solutions have not been adaptable to retrofit to existingspecialized optical devices in the form of a simple clip on typedevices.

As an example of a limitation of existing technology, consider thesystem outlined in GB 2472516. In this type of system a digital imagefrom a thermal camera is injected via a collimation optic into an I²objective optic. This has the effect that the digital thermal imagenecessarily must be the same color as that of I² phosphor. Thus both theI² image and the digital thermal image do not have good contrast and maynot be differentiated by their respective colors. As a second example,overlaying a thermal or symbology digital image onto an existingtelescopic sight (day sight) requires either a similar image injectioninto the day sight, thus causing a partial obscuration of the frontaperture, or considerable redesign and engineering of the eyepieceoptic. Therefore, there is a need in the industry to address one or moreof these issues.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a digital image overlay inan image intensified and/or telescopic sight (day sight) system. Brieflydescribed, the present invention is directed to an optical system foroverlaying a first image of a scene and a second image. The systemincludes a first imaging device providing the first image, a secondimaging device with an image display and collimation optics providingthe second image, and a waveguide. The waveguide has a first diffractiongrating configured to receive the first image, a second diffractiongrating configured to receive the second image, and a guide portiondisposed between the first diffraction grating and the seconddiffraction grating configured to convey the second image to the firstgrating. The first diffraction grating is configured to overlay thefirst image and the second image.

Other systems, methods and features of the present invention will be orbecome apparent to one having ordinary skill in the art upon examiningthe following drawings and detailed description. It is intended that allsuch additional systems, methods, and features be included in thisdescription, be within the scope of the present invention and protectedby the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The components in the drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the present invention. The drawingsillustrate embodiments of the invention and, together with thedescription, serve to explain the principles of the invention.

FIG. 1 is a schematic diagram of a first embodiment of an optical systemaccording to the present invention.

FIG. 2A is a schematic diagram showing a detailed view of the waveguideof FIG. 1.

FIG. 2B is a schematic diagram showing a side view of a waveguide havinggratings on opposite surfaces of the waveguide.

FIG. 3 is a schematic diagram of a second embodiment of an opticalsystem according to the present invention.

FIG. 4 shows a perspective view of the first embodiment of FIG. 1.

FIG. 5 is a flowchart of an exemplary embodiment of a method forcombining a first image and a second image with a planar waveguide.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers are used in thedrawings and the description to refer to the same or like parts.

As used within this description, “substantially” means “very nearly,” orwithin typical manufacturing tolerances.

FIG. 1 shows an exemplary first embodiment of the present inventiondirected to a system 100 for overlaying a digital image 152 of a scene101 with an image 151 produced by an optical device 110, for example, ananalogue optical device. For example, the first analogue optical device110 may include image intensified (I²) night vision optics, ortelescopic sight (day vision) optics. The overlaid digital image 152preferentially may be a digital thermal image, but may be another image,for example, another waveband image or symbology.

Under the first embodiment 100 the first optical device 110 may be, forexample, an I² night vision device that produces a first image 151 of ascene 101. For example, the first optical device 110 may receive lightfrom the scene 101 at an objective lens 112, and produce the first image151 for viewing at an eyepiece 115. The first image 151 may then passthrough the waveguide 145 and diffraction grating 141 unaltered. Thediffraction grating 141 may be designed in such a way as to allowtransmitting the first image 151 with only small transmission losseswhere the light is put into other diffraction orders. The first image151 may be viewable through a waveguide 140, for example, a slabwaveguide 140 by a viewer 180, for example, at a second planar surface146 of the waveguide opposite the first planar surface 145, behind thefirst diffraction grating 141.

The second optical device 120 may be, for example, a thermal imagingdevice that produces a second image 152 of the scene 101. For example,the second optical device 120 may receive long wave infrared radiation160 from the scene 101 at an objective lens 122, and produce the secondimage 152 of the scene 101, for example, a digital image via anelectrical connection 124 for viewing at a display 126. The display 126may be a micro OLED display to reduce overall system size, preferablyconfigured to provide a full range of colors in the visible spectrum,or, alternatively, may be configured to provide colors that contrast thecolor spectrum of the first image 151, which may be, for example a greenphosphor typical of an image intensified channel. For example, if thecolor content of the first image 151 is predominantly in the greenand/or yellow range, the display 126 may be configured to present imagesin the visible as red green and blue or combinations thereof (forexample to produce grayscale images).

At the display 126, the second image 152 may be collimated, for example,by a collimator 130 for introduction into the waveguide 140 through asecond diffraction grating 142 on a first planar surface 145 of thewaveguide 140. The first diffraction grating 141 and the seconddiffraction grating 142 may be coupled via the waveguide 140 such thatthe second image 152 may be conveyed via total internal reflection inthe waveguide 140 to be viewable through the waveguide 140 by the viewer180, for example, at the second planar surface 146 of the waveguideopposite the first planar surface 145, behind the first diffractiongrating 141, such that the second image 152 overlays the first image 151from the perspective of the viewer 180 to form a combined image 153, forexample, in a transparent mode. The combined image 153 may be referredto as a “fused image,” a “combined image,” and/or an “overlaid image.”

The first image 151 passes through the first diffraction grating 141 andthe waveguide 140 substantially unchanged. At the same time thediffraction grating 141 redirects the rays from the second image 152that have propagated down the waveguide to exit 140 in directionscoincident to the first image 151. The eye of the viewer 180 performs asimple addition of the two images 151, 152 because the two images 151,152 do not interfere with one another.

The magnification of the combined second optical device 120 and thecollimation optics 130 is preferably the same as the magnification ofthe first optical device (typically×1). This ensures that the images 151and 152 appear to have substantially the same size as seen by the viewer180.

The waveguide 140 may be thought of as the principal component of awaveguide assembly 140, 141, 142. When the gratings 141, 142 are coupledto the waveguide 140, for example, glued on with optical cement, amongother possible means, they change the direction of incoming light byputting most of the energy into a desired diffraction order. Typicallythe same diffraction grating may be used for both gratings 141, 142 inthe same orientation so that the direction of the incoming and outgoinglight is the same and the resulting image may be thought of as beingcoupled.

The first optical device 110 may be coupled to the waveguide 140 and/orthe first diffraction grating 141, for example, via a mechanism such asa clamping mechanism, a threaded coupler, or any other type of couplingmeans that provides mechanical alignment and structural robustness. Thesecond optical device 130 may similarly be mechanically coupled to thecollimation optics 130 so that the second image 152 is correctly alignedwith respect to the waveguide 140. In alternative embodiments, thecollimator 130 may be incorporated into the second optical device 120.

While FIG. 1 depicts the first diffraction grating 141 and the seconddiffraction grating 142 as both being on the first planar surface 145 ofthe waveguide 140, in alternative embodiments, the diffraction grating141 and the second diffraction grating 142 may both be on the secondplanar surface 146. Similarly, as shown by FIG. 2B, the diffractiongrating 141 and the second diffraction grating 142 may be positioned onopposite planar surfaces 145, 146 of the waveguide 140.

The first diffraction grating 141 and the second diffraction grating 142may preferably both be of the same type, for example, both reflectivediffraction gratings or both transmissive gratings. However, for someapplications the first diffraction grating 141 and the seconddiffraction grating 142 may differ in type, for example, one being areflective diffraction grating and the other being a transmissivegrating.

As used herein, “diffraction grating” 141, 142, may refer to a volumehologram integrated with the waveguide 140 to perform a diffractiveredirection of the light. The waveguide 140 may use other structuresapart from diffraction gratings/holograms, for example, a mirror forinput and beam splitter for output or prism structures, although thesemay be less desirable than diffraction gratings/holograms, which maygenerally be thinner.

FIG. 2A is a detail of the waveguide 140. The waveguide 140 ispreferably a planar waveguide or “slab” waveguide, having asubstantially rectangular cross section. The first planar surface 145and the second planar surface 146 may be substantially parallel over aheight H (or length), the first planar surface 145 and the second planarsurface 146 each having a width W, and being separated by a thickness Tof the waveguide 140. In general, the width W of the waveguide 140 isgreater than the thickness T of the waveguide. While FIGS. 1, 2A, and 2Bdepict the waveguide 140 as being generally planar, in alternativeembodiments the waveguide 140 may have gently curved surfaces 145, 146.The diffraction gratings 141, 142 may be typically orientated the sameway with respect to the direction of the periodic structure of thewaveguide 140, but this may not always be the case.

FIG. 2B is a schematic diagram showing a side view of the waveguide 140of FIG. 1. The waveguide 140 is configured according to the wavelengthsof the first image 151 and the second image 152 so that all diffractedrays that propagate along the waveguide 140 satisfy the total internalreflection condition of the optical material of the waveguide 140. Thewaveguide 140 may have a field of view in the range of 20 degrees to 50degrees, and be formed of a material having a low refractive index, forexample NBK7 optical acrylic, or having a high refractive index, forexample, N-SF11 depending upon the optical design and its application.An exemplary waveguide 140 may have a width in the range of 20-50 mm, alength (height) on the order of 30-100 mm, and a thickness in the rangeof 1-10 mm. The collimator 130 may have a diameter at a front end 132that is approximately the same size as the eyepiece 115 of the firstoptical device 110 or a front lens of the first optical device, forexample, a diameter of 20 mm, plus or minus 5 mm. The first image 151and the second image 152 by construction preferably have the samemagnification, for example, ×1 magnification. This ensures that the twoimages 151, 152 when aligned are overlaid with the same size.

As described above, combining the images 151, 152 at the waveguide 140allows for the first image 151 and the second image 152 to havedifferent and (preferably) contrasting color content, so that the viewer180 can differentiate the first image 151 and the second image 152. Incontrast, for example, combining images by injecting a digital thermalimage into the objective lens of an I² device will result in a firstimage and second image both having a similar color content, for example,predominantly green.

Under the first embodiment 100, the collimator 130 and the waveguide 140may be retrofitted to combine the first image 151 from an existing firstoptical device 110 and the second image 152 of an existing secondoptical device 120. For example, the collimator 130 and the waveguide140 may be configured to clip onto the existing first optical device 110and/or the second optical device 120.

The first optical system 110 and the second optical device 120 andcollimator optics 124 and display 126 are arranged to produce the samemagnification, for example ×1 magnification, so that the first image 151and the second image 152 have the same size. The first image 151 and thesecond image 152 may be aligned, for example bore sighted, to overlaythe second image 152 exactly on top of the first image 151. This may beachieved, for example, mechanically at manufacture time with in-houseexpertise and/or may be digitally realigned when in active use (forexample due to drift with time and usage).

FIG. 3 shows an exemplary second embodiment of the present inventiondirected to a system 300 for overlaying a generated image, for example,a digital image 252 with an image 151 produced by an optical device 110to provide a combined image 253. For example, the first optical device110 may be image intensified (I²) night vision optics, or telescopicsight (day vision) optics. The overlaid digital image may include, forexample, symbology (symbols that indicate one or more objects in ascene), or captions, among other types of digital images.

The second optical device 220 may include, for example, a digitaldisplay device 222 that produces the second image 252 to be overlaidwith the scene 101. For example, the second optical device 120 mayprovide the second image 252 via an electrical connection 224 forviewing at a display 226. The display 226 may be an OLED (organic lightemitting diode) display, preferably configured to provide a full rangeof colors in the visible spectrum, or, alternatively, may be configuredto provide colors that contrast the color spectrum of the first image151, which may be, for example a green phosphor typical of an imageintensified channel. For example, if the color content of the firstimage 151 is predominantly in the green, the digital imaging device 222may be configured to generate the second image 252 in the visible as redgreen and blue or combinations thereof (for example to produce grayscaleimages).

As with the first embodiment 100, under the second embodiment 300 thesecond image 152 presented by the display 226 may be collimated, forexample, by a collimator 228 for introduction into the waveguide 140through a second diffraction grating 142 on a first planar surface 145of the waveguide 140. The first diffraction grating 141 and the seconddiffraction grating 142 may be coupled via the waveguide 140 such thatthe second image 252 may be conveyed via total internal reflection inthe waveguide 140 to be viewable through the waveguide 140 by the viewer180, for example, at the second planar surface 146 of the waveguideopposite the first planar surface 145, behind the first diffractiongrating 141, such that the second image 252 overlays the first image 151from the perspective of the viewer 180 at the combined image 253.

Under the second embodiment, the digital imaging device 222 may positionsymbols and/or captions of the second image 252 appropriately withrespect to the first image 151 when they are overlaid by the waveguide140. Similarly, in alternative embodiments of the first embodiment,there may be a connection 350, for example, a mechanical, electrical, orelectromechanical connection between the second optical device 220 andthe first optical device 110, for example, to provide alignment controlbetween the first image 151 and the second image 152 (bore sighting).

Under the second embodiment 300, the second optical device 220(including the collimation optics 228) and the waveguide 140 may beretrofitted to combine the first image 151 from an existing firstoptical device 110 and the second image 252 of the second optical device220. For example, the second optical device 220 and the waveguide 140may be configured to clip onto the existing first optical device 110.

FIG. 4 shows a perspective view of the first embodiment. It should benoted that while FIG. 4 shows a bare waveguide 140 for clarity, in atypical application the waveguide 140 may be encapsulated appropriately(not shown) to provide a level of ruggedisation.

FIG. 5 is a flowchart 600 (described here with reference to the firstembodiment shown in FIG. 1) of an exemplary embodiment of a method forcombining a first image 151 and a second image 152 with a planarwaveguide 140 comprising a first coupler to a first diffraction grating141 in optical communication with the waveguide 140 and a second couplerto a second diffraction grating 142 in optical communication with thewaveguide 140.

It should be noted that any process descriptions or blocks in flowchartsshould be understood as representing modules, segments, portions ofcode, or steps that include one or more instructions for implementingspecific logical functions in the process, and alternativeimplementations are included within the scope of the present inventionin which functions may be executed out of order from that shown ordiscussed, including substantially concurrently or in reverse order,depending on the functionality involved, as would be understood by thosereasonably skilled in the art of the present invention.

A first image 151 is received from a first imaging device 110 by a firstinput coupler to the first diffraction grating 141, as shown by block610. A second image 152 is received from a second imaging device 120 bya second input coupler to the second diffraction grating 142, as shownby block 620. The second image 152 is conveyed from the seconddiffraction grating 142 to the first diffraction grating 141 via thewaveguide 140, as shown by block 630. The second image 152 and the firstimage 151 exit the waveguide to produce a combined image 153, as shownby block 640.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncover modifications and variations of this invention provided they fallwithin the scope of the following claims and their equivalents.

What is claimed is:
 1. An optical system for overlaying a first image ofa scene and a second image of the scene, comprising; a first imagingdevice comprising a first objective lens providing the first image; asecond imaging device comprising a second objective lens an imagedisplay, and collimation optics providing the second image; and awaveguide comprising: a first diffraction grating configured to receivethe first image; a second diffraction grating configured to receive thesecond image; and a guide portion disposed between the first diffractiongrating and the second diffraction grating configured to convey thesecond image to the first grating, wherein the first diffraction gratingis configured to overlay the first image and the second image.
 2. Thesystem of claim 1 wherein the first diffraction grating is configured tooverlay the first image and the second image in an effectivelytransparent mode.
 3. The system of claim 1 wherein the first diffractiongrating comprises an input coupler to the waveguide and the seconddiffraction grating comprises an output coupler from the waveguide. 4.The system of claim 3 wherein the first grating and/or the secondgrating comprises a reflective diffraction grating and/or a transmissivediffraction grating.
 5. The system of claim 1, wherein the first imagepredominantly comprises a first color and the second image predominantlycomprises colors other than the first color.
 6. The system of claim 1wherein the waveguide comprises a planar waveguide.
 7. The system ofclaim 6 wherein the waveguide comprises a substantially rigid structure.8. The system of claim 1 wherein the first imaging device is selectedfrom the group consisting of an analogue daylight optic and an imageintensified night vision device.
 9. The system as claimed in 1, whereinthe second imaging device comprises a a thermal camera.
 10. The systemas claimed in 9, wherein the second imaging device and the collimationoptics operate at one times magnification.
 11. A method for combining afirst image and a second image with a planar waveguide comprising afirst coupler to a first diffraction grating in optical communicationwith the waveguide and a second coupler to a second diffraction gratingin optical communication with the waveguide, comprising the steps of:receiving a first image of a scene by a first objective lens of a firstimaging device: receiving a second image of the scene by a secondobjective lens of a second imaging device; receiving the first imagefrom the first imaging device by a first input coupler to the firstdiffraction grating; receiving the second image from the second imagingdevice by a second input coupler to the second diffraction grating;conveying the second image from the second diffraction grating to thefirst diffraction grating via the waveguide; and overlaying the secondimage and the first image to produce a combined image.
 12. The method ofclaim 11, further comprising the step of providing visual access to thecombined image via an output coupler to the planer waveguide of thefirst diffraction grating.
 13. The system of claim 1, wherein a combinedmagnification of the second image by the second optical device and thecollimation optics is substantially the same as a magnification of thefirst optical device, and the first image of the scene and the secondimage of the scene appear to have substantially the same size as seen byviewer.